A "buck" or "step-down" switch-mode voltage regulator is one in which the output voltage is lower than its input voltage.
Note: A customer asked the origin of the term and no one seems to know! A buck regulator is a step-down regulator, as opposed to boost. We think it's an American term in England it was always "step-down."
Buck means to resist or reduce (as in "buck the trend"), and hence was used to denote a step-down. Conveniently, it alliterates with the opposite, a boost regulator.
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